The invention concerns equipment and a process permitting better combustion to be obtained of a gas specifically containing hydrocarbons. This equipment and process can be used, for example, in flares of a oil refinery or in oil and gas production fields, to burn the residual gases or the gaseous emissions without emissions of unburned hydrocarbons.
Oil processing in a refinery entails the production of residual gases and gaseous emissions, where the elimination by combustion in gas burning systems, called either xe2x80x9cflaresxe2x80x9d or xe2x80x9cgas flaresxe2x80x9d in the profession, can be the source of poisonous and malodorous emissions, smoke or noise, harmful to the environment.
These nuisances and notably those contributed by the incomplete combustion of gas, for example, rich in hydrogen sulfide (H2S), generally appear, when the quantity of air necessary for perfect combustion is insufficient, that is to say when the ratio between the flow of gas to be burned and the air flow necessary for combustion is less than the stochiometric ratio, and when the three conditions necessary for optimal combustion, called xe2x80x9cthe three T""s,xe2x80x9d namely the Temperature of the flame, the Time of air/gas mixing before burning and the Turbulence applied to this mixture, are insufficiently met.
It is generally due to the fact that the excess of gas to burn has a relatively low pressure and a high flow which can reach up to 10,000,000 Sm3/day, arising, for example from an operational failure of an oil refining unit or on an oil or gas production site. Since the pressure of the gas to burn remains low overall, this does not permit a sufficiently active aeration of the flame by the gas pressure at the outlet of the feed tube of the flare. The fuel-comburant mixture in the combustion zone becoming deficient in the air content necessary for a perfect combustion therefore requiring an external contribution of comburant by any means available in the technology to improve the gas combustion.
Up till now, injection devices have been relied upon, fed, for example, by steam traversing the injectors, or other motive fluids such as air or gas, that inducts air and the necessary turbulence for the combustion. However, these devices have the low performances, which requires using significant quantities of fluids to compensate for their lack of efficiency.
It turns out, in a refinery, for example in the case of using steam as a motive fluid, a heavy consumption has the effects of:
a significant noise emission, due to the passage of the steam in tubes and injectors;
a cooling of the flame, that does not permit ensuring the correct conditions for gas combustion, for example the acidic gases such as H2S, where a temperature of 700xc2x0 C. required for its complete oxidation is not attained, under these conditions, thus producing some toxic and malodorous emissions;
an energy balance of the site may show a deficit, since it depends on the production of steam.
Generally there is no steam available on the oil and gas production fields, and the pressure of the gas to be burned is too low to be used as source of sufficient mixing power for the fuel/comburant. Therefore, the combustion of waste, that is gases rich in hydrocarbons and sometimes liquid hydrocarbons, called condensates, is incomplete and usually accompanied by thick black smoke.
GB 1 323 674 describes an equipment of the flare type, supplied with a combustion gas by at least one input tube of the gas to be burned. The end of the tube is surrounded with a multiplicity of devices arranged around it and each containing a venturi and a motive fluid feed,
FR 573 059 describes a blowing equipment in which a fluid under pressure is used to entrain another fluid and impart speed to it. A multiplicity of motive fluid feed tubes are arranged in an essentially annular fashion around the axis of at least one venturi, so as to suck in the second fluid before injection into a combustion zone.
U.S. Pat. Nos. 1,443,315 A and 3,554,681 also describe devices in which injection devices of a first gas, arranged in crown at the input of a venturi, entrains a second gas into it.
The builders of flares have also considered a solution that consists, for example, of bringing air into the combustion zone by means of groups of high power fans, arranged for example under the flare, and to stagger the gas distribution with the help of automatic valves controlled by complex instrumentation. This solution proves to be applicable only with difficulty, since there are high investment costs and operation costs, and besides, it is rendered somewhat unreliable by the installation of fans under the flame in a hot and corrosive atmosphere, and also raises safety problems due to the possible falling of easily inflammable liquid hydrocarbons on the hot fans.
The Applicant therefore did a search with a view to finding solutions that are, both satisfactory on the technical level, simple, reliable and where the corresponding investment cost is low, either in a refinery and on a production site, to obtain smokeless combustion of a gas which can contain some liquid hydrocarbons.
The Applicant has thus succeeded in improving a gas flare type of equipment, so as to facilitate the combustion of fuel gases in the atmosphere, containing a combustion zone supplied with at least one fuel gas for at least one input tube of the gas to be burned, the end of the said tube being surrounded with a multiplicity of devices arranged around this end and each composed of a venturi and a motive fluid feed, this equipment being characterized:
in that each of devices includes a multiplicity of tubes arranged in an essentially annular fashion around axis AA of the venturi;
and in that the set of tubes of each device, which injects the motive fluid into the venturi, diverge from one another forming an angle xcex1 with the axis AA of the venturi, greater than 3xc2x0 and preferably essentially equal to the angle that forms the divergent flare of the said venturi with said axis.
This equipment has the major advantage of permitting a smokeless combustion, even when the gas pressure is low and the flow high and it contains some liquid hydrocarbons.
The invention also has as its object the use of the equipment defined above to facilitate the combustion in a combustible gas atmosphere feeding the gas input tube, while tubes of devices for input of the motive fluid are fed by a fluid chosen from the groups constituted by air, air enriched with oxygen, steam or a combustible gas, this use being characterized in that that the pressure of the motive fluid is comprised between 0.5 and 6.105 Pa, preferably, between 1 and 3.105 Pa, and in that each tube transports between 1% and 33% and, preferably, between 5% and 33% of this motive fluid.
This use eliminates resorting to fans as well as the resultant noise from the passage in the injectors of a fluid such as steam.
In addition to a complete, smokeless combustion, the equipment of the invention permits, on the one hand, decreasing the consumption of the motive fluid, for example steam, and, on the other hand increasing the reliability of the facility by the absence of moving parts, such as fans, so as to have a process that is easily implemented, and involves installation and operational costs that are relatively low.
Other advantages and features of the equipment and the process according to its invention come from following the present description, which will refer to FIGS. 1 to 3 of the attached drawings, that do not have a restrictive character.